As a conventional connection structure for this kind of covered wires, a structure designed by this inventor (see Japanese Laid-Open Patent Application No. 7-320842) will be described.
For connecting two covered wires the outer periphery of which is coated with a cover portion made of resin, at their intermediate connection portions, a pair of resin chips which are of resin material, a horn for producing ultrasonic vibration, and an anvil for supporting the covered wires and resin chips at the time of connection are utilized. The anvil includes a base stand and a support portion projecting from the base stand. The support portion is designed in a substantially cylindrical shape. The support portion has a bore portion which is opened at the opposite side to the base stand side. Two pairs of grooves are formed on the peripheral wall of the support portion so as to cross with each other substantially at the center of the bore portion. The four grooves are formed so as to open on the same side as the bore portion, extending along the projection direction of the support portion and intercommunicating with one another through the bore portion.
The pair of resin chips are designed in a disc shape having a slightly smaller outer diameter than the diameter of the bore portion of the anvil. Furthermore, an end face of a head portion of the horn is designed in a disc shape having an outer diameter which is substantially equal to or slightly smaller than that of the resin chips.
In order to connect the two covered wires to each other, both of the covered wires are overlapped with each other at the connection portion thereof and the overlapped connection portions are pinched by the pair of resin chips from the upper and lower sides of the connection portions. Specifically, one of the resin chips (the resin chip at the lower side) is inserted into the bore portion of the anvil such that the melting surface thereof is directed upward. Then, one covered wire is inserted into the pair of confronting grooves from the upper side of the inserted resin chip. Then, the other covered wire is inserted into the other pair of the confronting grooves. Finally, the other (upper side) resin chip is inserted such that the melting surface is directed downward. The covered wires are arranged in the bore portion so that the respective connection portions thereof cross each other at the center of the bore portion. Through this arrangement, the connection portions of the covered wires are pinched substantially at the center of the melting surfaces of the upper and lower resin chips respectively in the overlapping direction.
Subsequently, the cover portions at the connection portions of the covered wires are melted so as to be dispersed by ultrasonic vibration. Furthermore, the conductive wire portions (core) of the covered wires are conductively contacted with each other at the connection portion by pressurizing the covered wires from the outside of the resin chips. Thereafter, the pair of the resin chips are mutually melt-fixed at the melting surfaces to seal the connection portion.
Specifically, the head portion of the horn is inserted into the bore portion from the upper side of the finally-inserted upper (other) resin chip and placed on the upper resin chip to excite and pressurize the connection portions of the covered wires from the outside of the upper and lower resin chips between the horn and the anvil. The cover portions are first melted and the conductive wire portions of the covered wires are exposed at the connection portion between the resin chips. At this time, the melted cover portions are extruded from the center side of the resin chips toward the outside thereof because the connection portions are pressurized from the upper and lower sides, so that the conductive wire portions are more excellently exposed and surely conductively contacted with each other. Like the pressurizing direction, the direction of the excitation of the connection portions is set to be coincident with the overlapping direction of the covered wires, so that the action of extruding the melted cover portions from the center side of the resin chips to the outside thereof is promoted.
When the pressurizing and exciting operation on the connection portions is further continued after the melting of the cover portions, the resin chips are melted and the confronting melting surfaces of the resin chips are melt-fixed to each other. In addition, the outer peripheral surface portions of the cover portions which are adjacent to the conductively contacted conductive wire portions and the resin chips are melt-fixed. With this operation, the outer peripheral portions of the conductively-contacted conductive wire portions are kept to be coated with the resin chips.
However, in the above described structure, a soft conductive wire portion exposed by dispersing the cover portion is contacted with corners of the resin chips at introducing ends of the covered wire, such that melted resin covers and seals a portion between the corners of the resin chips and the cover portion. Thus, if pressurizing and excitation of the horn are increased too much to secure a sufficient melting force, the corners of the aforementioned introducing ends are strongly pressurized by the conductive wire portion when the upper and lower resin chips are melted together, so that the conductive wire portion may be damaged by the corners. Thus, to secure sealing condition of the resin chips and prevent the conductive wire portion from being damaged, it is necessary to set a melting condition (e.g., ultrasonic energy, pressure, pressurizing and excitation time, etc.) by pressurizing and excitation in details and manage it. Thus, the melting work is very complicated.